PROJECT SUMMARY Calorie restriction (CR) is a promising nutritional strategy that has the potential to attenuate the risk of age- related disease. The National Institutes of Health-funded CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) was the first clinical trial to demonstrate the feasibility of achieving sustained, moderate CR in healthy, non-obese adults. Remarkable reductions in cardiometabolic risk factors were observed in the CR group compared with the ad libitum intake control group. Over the two-year study period, participants were prescribed a caloric intake target but self-selected their diet, and notable variability was observed in objectively measured adherence to CR. Examining diet composition during CR compared to ad libitum intake will help identify factors that may contribute to this variability. Emerging evidence suggests that the ratio of macronutrients in the diet plays an important and independent role in influencing health. Studies in mice indicate that a low-protein, high-carbohydrate diet is associated with a longer healthspan. This observation contradicts findings of greater satiety and lower energy intake associated with a higher protein diet. As higher protein intake likely supports adherence to a CR regimen, further research is needed to determine whether dietary composition can be optimized for both longer healthspan and CR adherence. The proposed research directly contributes to the NIH FOA PA-18-824 and will use CALERIE data to evaluate the effect of dietary composition on adherence to CR and resultant cardiometabolic disease risk factor modification. The publicly available CALERIE database includes comprehensive measures of self-selected diet composition, an objective measure of caloric intake, and a variety of health outcomes including inflammatory and cardiometabolic risk factors. We will use the Geometric Framework for Nutrition (GFN), a state-of-the-art analytical approach that can simultaneously evaluate multiple dietary components and determine their associations with disease risk. Identifying these dietary factors has important implications for optimizing adherence to CR and for the prevention and treatment of age-related chronic disease. We hypothesize that dietary components associated with successful CR in a non-obese, disease-free population will confer even stronger benefits in individuals at risk for cardiometabolic disease, such as populations with overweight or obesity. Our long-term goal is for our results to inform dietary intervention strategies to facilitate CR, attenuate cardiometabolic risk, and reduce the burden of age-related chronic disease.